Various medical conditions, diseases and dysfunctions may be treated by ablation, using various ablation devices and techniques. Ablation is generally carried out to kill or destroy tissue at the site of treatment to bring about an improvement in the medical condition being treated.
In the cardiac field, cardiac arrhythmias, and particularly atrial fibrillation are conditions that have been treated with some success by various procedures using many different types of ablation technologies. Atrial fibrillation continues to be one of the most persistent and common of the cardiac arrhythmias, and may further be associated with other cardiovascular conditions such as stroke, congestive heart failure, cardiac arrest, and/or hypertensive cardiovascular disease, among others. Left untreated, serious consequences may result from atrial fibrillation, whether or not associated with the other conditions mentioned, including reduced cardiac output and other hemodynamic consequences due to a loss of coordination and synchronicity of the beating of the atria and the ventricles, possible irregular ventricular rhythm, atrioventricular valve regurgitation, and increased risk of thromboembolism and stroke.
As mentioned, various procedures and technologies have been applied to the treatment of atrial arrhythmias/fibrillation. Drug treatment is often the first approach to treatment, where it is attempted to maintain normal sinus rhythm and/or decrease ventricular rhythm. However, drug treatment is often not sufficiently effective and further measures must be taken to control the arrhythmia.
Electrical cardioversion and sometimes chemical cardioversion have been used, with less than satisfactory results, particularly with regard to restoring normal cardiac rhythms and the normal hemodynamics associated with such.
A surgical procedure known as the MAZE III (which evolved from the original MAZE procedure) procedure involves electrophysiological mapping of the atria to identify macroreentrant circuits, and then breaking up the identified circuits (thought to be the drivers of the fibrillation) by surgically cutting or burning a maze pattern in the atrium to prevent the reentrant circuits from being able to conduct therethrough. The prevention of the reentrant circuits allows sinus impulses to activate the atrial myocardium without interference by reentering conduction circuits, thereby preventing fibrillation. This procedure has been shown to be effective, but generally requires the use of cardiopulmonary bypass, and is a highly invasive procedure associated with high morbidity.
Other procedures have been developed to perform transmural ablation of the heart wall or adjacent tissue walls. Transmural ablation may be grouped into two main categories of procedures: endocardial and epicardial. Endocardial procedures are performed from inside the wall (typically the myocardium) that is to be ablated, and is generally carried out by delivering one or more ablation devices into the chambers of the heart by catheter delivery, typically through the arteries and/or veins of the patient. Epicardial procedures are performed from the outside wall (typically the myocardium) of the tissue that is to be ablated, often using devices that are introduced through the chest and between the pericardium and the tissue to be ablated. However, mapping may still be required to determine where to apply an epicardial device, which may be accomplished using one or more instruments endocardially, or epicardial mapping may be performed. Various types of ablation devices are provided for both endocardial and epicardial procedures, including radiofrequency (RF), microwave, ultrasound, heated fluids, cryogenics and laser. Epicardial ablation techniques provide the distinct advantage that they may be performed on the beating heart without the use of cardiopulmonary bypass.
When performing procedures to treat atrial fibrillation, an important aspect of the procedure generally is to isolate the pulmonary veins from the surrounding myocardium. The pulmonary veins connect the lungs to the left atrium of the heart, and join the left atrial wall on the posterior side of the heart. When performing open chest cardiac surgery, such as facilitated by a full sternotomy, for example, epicardial ablation may be readily performed to create the requisite lesions for isolation of the pulmonary veins from the surrounding myocardium. Treatment of atrial ablation by open chest procedures, without performing other cardiac surgeries in tandem, has been limited by the substantial complexity and morbidity of the procedure. However, for less invasive procedures, the location of the pulmonary veins creates significant difficulties, as typically one or more lesions are required to be formed to completely encircle these veins.
One example of a less invasive surgical procedure for atrial fibrillation has been reported by Saltman, “A Completely Endoscopic Approach to Microwave Ablation for Atrial Fibrillation”, The Heart Surgery Forum, #2003-11333 6 (3), 2003, which is incorporated herein in its entirety, by reference thereto. In carrying out this procedure, the patient is placed on double lumen endotracheal anesthesia and the right lung is initially deflated. Three ports (5 mm port in fifth intercostal space, 5 mm port in fourth intercostal space, and a 10 mm port in the sixth intercostal space) are created through the right chest of the patient, and the pericardium is then dissected to enable two catheters to be placed, one into the transverse sinus and one into the oblique sinus. Instruments are removed from the right chest, and the right lung is re-inflated. Next, the left lung is deflated, and a mirror reflection of the port pattern on the right chest is created through the left chest. The pericardium on the left side is dissected to expose the left atrial appendage and the two catheters having been initially inserted from the right side are retrieved and pulled through one of the left side ports. The two catheter ends are then tied and/or sutured together and are reinserted through the same left side port and into the left chest. The leader of a Flex 10 microwave probe (Guidant Corporation, Santa Clara, Calif.) is sutured to the end of the upper catheter on the right hand side of the patient, and the lower catheter is pulled out of a right side port to pull the Flex 10 into the right chest and lead it around the pulmonary veins. Once in proper position, the Flex 10 is incrementally actuated to form a lesion around the pulmonary veins. The remaining catheter and Flex 10 are then pulled out of the chest and follow-up steps are carried out to close the ports in the patient and complete the surgery.
Although advances have been made to reduce the morbidity of atrial ablation procedures, as noted above, there remains a continuing need for devices, techniques, systems and procedures to further reduce the invasiveness of such procedures, thereby reducing morbidity, as well as potentially reducing the amount of time required for a patient to be in surgery, as well as reducing recovery time.